My 4runner has been squealing on startup for a while now but it seems to be getting worse with colder weather. Shortly after I got it last year, the abs, trac off, vsc, and e brake light all went on with an alarm as well and shortly after it went away and hasn't happened again since. Reason I mention this: this squealing on startup usually goes away once warm and only happens very infrequently when I brake after it's warm. The squealing however goes away on startup if I push the brake pedal, but immediately starts up again after. Any ideas what this could be?

Getting my serpentine belt replaced in a couple days because it needs to be replaced anyway but I don't think that's the problem.

 

Sounds like an idler pulley bearing. They are prone to seizing up when they get old, and they squeel when they do. Not on the timing belt, but one of the other belts. Just pull all the utility belts off, and spin their idler pulleys, and see if on sounds/feels like it's grinding, or otherwize like a bad bearing. They're readily available, and easy to replace. Give them a look, and see if maybe one's gone south on you.

Worth a look, anyway...
Pat☺